SOFIA, BULGARIA — Drones struck two merchant ships off Bulgaria's Black Sea coast overnight into Tuesday, sinking one of them, Prime Minister Rumen Radev said — the second such attack in the same stretch of water in a week and the latest sign that the Russia-Ukraine war's shipping conflict is spilling into NATO territory.

The strikes hit around 1:30 a.m. local time roughly 20 nautical miles off the coast near Krapets, according to Al Jazeera. The Maltese-flagged, Ukrainian-owned cargo ship Chelsea 3 was hit by three aerial drones on its deck and hull; all 15 crew members — seven Ukrainians and eight Azerbaijanis — were evacuated, with five treated for minor injuries. A second vessel sank; at least one crew member from that ship was rescued.

It is the second drone attack in the same waters in eight days. On Oct. 6, drones struck two ships in the same zone, sinking a Togo-flagged vessel; Bulgaria later called off the search for roughly ten missing crew members with no survivors found, per Al Jazeera's earlier report. A separate drone strike also set fire to a Turkish-owned cargo ship off Romania's coast on Monday, killing two of its crew.

"THE OUTCOME BENEFITS THE RUSSIAN FEDERATION."

Radev convened an emergency meeting of Bulgaria's Security Council, calling the attack "absolutely unacceptable" and noting it struck "in the immediate vicinity of Bulgarian territorial waters." While he said there was "no clear evidence" yet of who was responsible, he added that "the outcome benefits the Russian Federation" and said he would summon Russia's ambassador, Eleonora Mitrofanova, over the incident. Bulgaria is formally requesting assistance from NATO and the European Union.

Brussels and Kyiv point to Moscow

European Commission President Ursula von der Leyen said "the Black Sea has become another front of escalation of the Russian war in Ukraine," adding, "We stand with Bulgaria. Those responsible should be held accountable." Ukrainian Foreign Minister Andrii Sybiha went further on social media, accusing Moscow of "deliberate disregard for civilian lives and maritime security" and calling the Black Sea a "lifeline for global food security," while urging allies to tighten sanctions on Russia. Russia had not commented publicly as of Tuesday.

Bulgaria, a NATO and EU member, sits along one of the most vital commercial shipping corridors for both Russian and Ukrainian trade, and hybrid, attribution-murky attacks on commercial vessels in the Black Sea have escalated sharply in recent weeks. No group has claimed responsibility for either the Oct. 6 or Oct. 13 strikes, and Radev's government says an investigation is underway.